The present invention relates to a micromechanical yaw rate sensor, having a substrate that has an anchoring device provided on the substrate, and having an annular flywheel that is connected, via a flexural spring device, with the anchoring device in such a way that the area of connection with the anchoring device is located essentially in the center of the ring, so that the annular flywheel is able to be displaced, elastically from its rest position, about an axis of rotation situated perpendicular to the substrate surface, and about at least one axis of rotation situated parallel to the substrate surface.
Yaw rate sensors are known from M. Lutz, W. Golderer, J. Gerstenmeier, J. Marek, B. Maihxc3x6fer, and D. Schubert, xe2x80x9cA Precision Yaw Rate Sensor in Silicon Micromachiningxe2x80x9d; SAE Technical Paper, 980267, and from K. Funk, A. Schilp, M. Offenberg, B. Elsner, and F. Lxc3xa4rmer, xe2x80x9cSurface-micromachining of Resonant Silicon Structuresxe2x80x9d; The 8th International Conference on Solid-State Sensors and Actuators, Eurosensors IX, Stockholm, Sweden, 25-29 Jun. 1995, pp. 50-52.
FIG. 2 shows a schematic top view of a known micromechanical yaw rate sensor.
In FIG. 2, the character 100 designates a substrate in the form of a silicon wafer. 10 designates an annular flywheel; 15, 15xe2x80x2 designate flexural sensors; 25 designates a bridge; 18, 18xe2x80x2 designate a respectively curved flexural spring, and 20, 20xe2x80x2 designate a base. The latter parts are manufactured from polysilicon over a silicon oxide layer, the silicon oxide layer being removed later in the process through undermining, in order to form the parts so that they can be displaced in relation to substrate 100. Only the two bases 20, 20xe2x80x2 are anchored on the substrate over the silicon oxide layer, and form fixed points of the sensor structure.
The functioning of the yaw rate sensor constructed in this manner is based on the principle of the law of conservation of angular momentum of a rotating system.
In general, the following holds:             M      _        =                            J          ·                                    ⅆ              ω                                      ⅆ              t                                      _            xc3x97              Ω        _              ,
where M is the moment of deviation, J is the mass moment of inertia, dxcfx89/dt is the angular velocity of the rotary oscillation, and xcexa9 is the sought yaw rate.
If, in the known yaw rate sensor according to FIG. 2, annular flywheel 10, which is rotating about the z axis, is rotated about its y axis, this flywheel performs a rotation about the x axis. Given a constant angular velocity about the z axis, this rotation about the x axis, which is caused by the above moment of deviation M, is directly proportional to the sought yaw rate xcexa9.
In general, the problematic on which the present invention is based is that the first three natural frequencies corresponding to the x, y, and z axes, indicated in the Figure, do not have a position that is optimal or that can be optimized easily in the context of a process.
In particular, a modification of the sensor mass for the adjustment of the first three natural frequencies is undesirable, because this has effects that are disturbing with respect to measurement technology.
The underlying idea of the present invention is that the anchoring device has two bases, situated opposite one another, that are connected fixedly with the substrate and are connected with one another via a bridge. A V-shaped flexural spring of the flexural spring device is attached to each of the opposed sides of the bridge in such a way that the apex is located on the bridge, and the limbs are spread out towards the flywheel with an opening angle.
The first natural frequency about the z axis can be set by determining the spring width and spring length of the V-shaped flexural springs, corresponding to the operating frequency in the forced mode of the sensor. By modifying the opening angle between the respective spring limbs, the detection resonance frequency of the sensor, i.e., the rotation out of the plane of the substrate about the x or y axis, can be set. The ratio of the natural frequencies to one another determines, to a considerable extent, the sensor properties, such as for example sensitivity, immunity to interference, and temperature stability.
The inventive micromechanical yaw rate sensor therefore has, in relation to the known solutions, the particular advantage that via the opening angle, or the width and length, of the V-shaped flexural springs, the natural frequencies can be adjusted in a simple and precise manner, independently of one another.
According to a preferred development, the opening angle is equal for both V-shaped flexural springs of the flexural spring device. Thus, only one angle need be optimized for the natural frequencies.
According to a further preferred development, the V-shaped flexural springs of the flexural spring device are attached to the bridge in such a way that they form an X shape. This creates a symmetrical shape of the flexural springs.
According to a further preferred development, the opening angle is selected such that the natural frequency about the axis of rotation situated perpendicular to the surface of the substrate is smaller than each natural frequency about an axis of rotation situated parallel to the surface of the substrate. In this way, an extraordinarily positive acquisition characteristic can be achieved.
According to a further preferred development, the bases at the opposed sides are fashioned with a wedge shape. Here, the bridge connects the two wedge tips with one another. In this way, the sensor obtains a good capacity for displacement about the z axis.
According to a further preferred development, the bridge is suspended freely over the substrate.
According to a further preferred development, it can be manufactured using silicon surface micromechanical technology. The use of surface micromechanical technology to manufacture the inventive micromechanical yaw rate sensor, specifically the series production process having a thick epipoly layer, typically 10 xcexcm thick, enables the formation of a rigid sensor structure, which enables a low cross-sensitivity to be achieved.